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Can sharks detect colour? And if so, are you better off wearing particular colours when you go swimming?—Parker

Don't ask a shark if your swimsuit brings out the colour of your eyes.

You'll get a similarly blank response from a dolphin or a whale.

That's because all these animals are effectively colourblind, says sensory neurobiologist Dr Nathan Hart from the University of Queensland, who has been studying the evolution of vision in sharks and other animals.

It all comes down to the photoreceptors they've got in the retinas of their eyes.

Like humans, sharks have both rods and cones in their retinas that are stimulated by light.

In humans, cones also have a secondary function — allowing us to see colour.

"We see colour obviously through a variety of neural processes, but primarily because we have three different cone types in the retina — red, green and blue," says Hart.

It's by comparing the amount of light signalled by these different visual pigments that we get our colour vision, he says.

"So if the blue gets more than the red for example, that's computed as a colour sensation."

Early research on shark species such as cat sharks which live in deeper water and have small eyes with mostly rods in their retina, suggested that sharks have predominantly nocturnal vision and probably no colour vision, says Hart.

But even species of shark which have quite high cone numbers, like the common black tip shark and the bull shark, can't see colour.

"Despite their high cone number they don't seem to have more than one cone type in the retina," says Hart.

This means they can see well in daylight, but Hart's research suggests they can't distinguish colours — everything is in black and white.

The only way animals like sharks, dolphins and whales could have some form of colour vision, says Hart, would be if the visual pigment in their rods was different to the one in their cones, and they could compare the differences in signals between the two.

Tips for swimmers

Although they can't see you in colour, Hart does have some tips for how to make yourself less attractive to sharks when you go swimming.

Sharks are only going to approach if they're curious, or if something looks a bit like food.

"If you could reduce your contrast against the surface of the water, as viewed from below, that might help," he says.

"Imagine you're a big fish or a seal swimming at the surface and a shark is underneath you, it's just going to see this black silhouette."

So while it kind of doesn't matter what colour you're wearing, Hart says, having a very reflective underside, or somehow matching the background, would make you less visible to the shark.

Some fish, for example, have fluorescent photophores, or light-emitting organs on their underside, which matches the light penetrating the water, removing their silhouette and making them less visible.

Shark-deterrent bikinis with light-emitting diodes? I can see them on the Parisian catwalks now.